Stretchable creped mica foil and method therefor

ABSTRACT

Method of producing stretchable creped mica foil includes depositing a mica suspension upon a web of creped material selected from the group consisting of fiber paper and textile material and subsequently drying the mica suspension on the web; and foil produced thereby.

United States Patent Rotter [4 1 May 2, 1972 [54] STRETCHABLE CREPED MICA FOIL AND METHOD THEREFOR [56] References Cited [72] Inventor: Hans-Werner Rotter, Numberg. Germany UNITED STATES PATENTS [73] Assignee: Siemens-Schuckert erk Akt engm lse flfi, 2,763,315 9/1956 Berberich et a1. 161/163 Berlin-Siemensstadt, Erlangen, Germany 2,077,438 4/1937 Rowe [22] Filed: Sept. 20 1966 3,101,845 8/1963 Heasley 161/163 [21] Appl. No.: 580,830 FOREIGN PATENTS OR APPLICATIONS Remed us. Application Data 1,061,688 7/1959 Germany ..161/163 [63] Continuation of $61. No. 174,462, Feb. 20, 1962, Primary Examiner-William J, Van Balen abandoned; Attorney-Curt M. Avery [30] Foreign Application Priority Data [57] ABSTRACT Feb. 24, 1961 Germany ..S 72704 Method of producing stretchable reped mica foil includes depositing a mica suspension upon a web of creped material [52] 0.8. CI. ..l6l/128, 156/622, 150/183, l d from the group consisting of fiber paper and textile 161/129 161/163, 161/171 162/112 material and subsequently drying the mica suspension on the [S1 Int. Cl. ..B32b 19/00, B32b 3/28, B32b 5/16 and f il produced thereby [58] Field of Search ..162/l 12,145; 156/53, 56, 62.2,

12 Claims, 4 Drawing Figures PATENTEDMY 2 I912 FIG. I

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FIG. 3

FIG. 2

STRETCHABLE CREPED MICA FOIL AND METHOD THEREFOR This application is a streamline continuation of Ser. No. 174,462 filed Feb. 20, 1962 and nowabandoned.

My invention relates to a method for producing mica foils suitable for electric insulating purposes, and to the products thereof.

Mica can be reduced to fine scales from which foils are made by a process similar to that used for producing a web of paper. However, this method involves difficulties not encountered in the production of paper from fibrous raw material. In paper manufacture, the fibers are always interfelted so that often considerable strength is obtained even in the wet condition of the product, this depending upon the type and length of the fibers. Paper, therefore, can be fabricated by rollers, presses and the like while still in wet condition. Thus, paper can be deformed, for example, to crepe.

Creped webs of paper have a greatly increased stretchability and can therefore be used to advantage for the insulation of electric bus bars or conductor rods for the rotors of electric machines. For such purposes the electric conductors can be wrapped up in creped paper and subsequently treated 'with casting resin.

However, for many electric insulating purposes the use of mica is indispensable. Mica splittings, such as those employed for micafolium, a cellulose paper of 30 to 50 g/m coated with one or two layers of split mica and provided with a layer of bonding or cementing agent, always tend to crack and split. This is a serious disadvantage, particularly for high-voltage windings. Mica foil does not possess these disadvantages, but does not have sufiicient ductility or stretchability and thus can be fabricated or deformed only with great difi'iculty. A deforming treatment of wet mica foil by mechanical deform ing methods is not feasible because, when mica particles are fabricated to form a mica foil, no interfelting is involved. Rather, there occurs a cementing efiect which takes place only when the product is being dried. In wet condition the material has zero strength (wet strength kg/mm). In dry condition it has relatively high strength (dry strength 3 kglmm A shaping of the wet mica foil by known deforming methods is not possible.

The production of mica foils by subjecting a mica suspension to suction on a web of paper or fabric placed upon a screen is described in German Pat. No. 1,061,688.

I have discovered that a mica foil of great strength and stretchability can be produced, a creped mica foil in particular, by employing, in lieu of ordinary paper, a creped fiber paper or creped web or fabric to support the suspension of mica on a screen. while the suspension is being subjected to suction for removing the water from the suspension or pulp. The flakes of mica deposit on the crepe web and adapt themselves to the folds and creases of the web. The mica foil thus contained in the creped web is thereafter dried and can be pulled off. The pulled-off mica foil has the same shape and form as the supporting web. Thus, when a creped web of paper or fabric is used for supporting the mica pulp during the operation, the resulting mica foil is likewise creped. The resulting creped mica foil can be further fabricated alone or together with the supporting web of paper or fabric, the latter being then left adherent to the mica foil in the further processing.

The invention may be further described with reference to the following examples.

EXAMPLE I A sheet of creped filter paper is placed upon a screen support, for example of 300 mm width and 1,000 mm length. The web is dampened and then tightly joined with, or caused to adhere to, the screen support by suction. Thereafter, a mica pulp greatly diluted with water, and containing about 25 g solids per liter, is poured onto the creped paper. The mica scales uniformly distribute themselves over the crepe paper web, and then adhere to the web, which is kept under negative pressure by suction applied to the opposite side of the screen. The mica deposits follow the hills and dales or valleys caused by the creping of the paper, in uniform distribution. The crepe paper inclusive of the mass of mica now attached thereto is lifted from the supporting screen and deposited upon a drying sheet, in 50 to 60 layers stacked above one another. The stack of layers is then dried in a drying press at C within 2 hours.

The resulting mica sheets constitute creped mica foils. They can now be pulled off the paper web or they can be further fabricated together with the web.

EXAMPLE ll An endless belt of screening material, which is kept in rotation, is provided with a creped, likewise endless web of paper or fabric which is kept attached to the screening material by suction and is thereby conveyed together with the screening belt. The web, kept under slight negative pressure, is charged with a uniform supply of mica pulp containing 20 to 30 g solids per liter. Due to the negative pressure, the mica particles are finally sucked against the supporting creped web while maintaining the unevenness of the web surface. The endless web is lifted off the screening belt at the reversing location of the belt, and then passed through a drying zone until the newly formed, creped mica foil is dry and sufficiently strong to be lifted off the web. The mica foil can then be coiled in the shape of a roll. The thickness of the mica foils is adjusted by correspondingly controlling the rotating speed of the endless screening belt. Reducing the travel speed of the belt results in depositing more mica per unit area. The thicker mica layer, however, requires a longer dwelling time in the drying zone.

The creped mica foils produced according to the invention can be directly wound into the shape of insulating parts and can be impregnated, for example in vacuum, with casting resin or the like. They can also be impregnated with impregnating varnish and binding agent, for example with silicone resin, shellac, epoxy resin, and can then be wound into spirals or coils or other shaped bodies or placed in flat sheets upon each other to form plates, which can be hardened hot under pressure.

windings made with creped mica foil produced according to the invention possess improved adaptability to the shape of the core body upon which the foil is wound. When laminated bodies are produced from creped mica foil made according to the invention, an improved bonding between the laminations is obtained superior to that obtained when smooth paper is used in production of the mica foil.

FIG. 1 of the drawing shows a suitable apparatus for carrying out a continuous manufacturing process. The forming device is a drum structure 14 comprising four separate sectorshaped cells. In operation, the drum structure is continuously rotated clockwise so that each cell passes sequentially through the positions a, b, c, d. In the position a, the cell is immersed in a bath of mica pulp 7 contained in a storage tank 6 and kept well mixed by a stirrer 8. Each cell has one or more openings 15. The openings of the cells located at a, b and c communicate with a suction pipe 5 through a stationary passage 16 extending over approximately three-quarters of a circle about the drum axis. In the position d, however, each cell communicates through its opening or openings with a passage 17 that extends over approximately one-quarter of the circle and leads either out into the ambient air or to an air blower or other supply of positive gas pressure.

An endless belt 9 of water-permeable web material, that is, crepe paper, is guided by rollers 10 around the suction drum 14. The circumferential wall of the drum structure consists of a wire mesh or other screening material so as to form a sieve in accordance with the foregoing explanation. Due to the vacuum in the cells located at a, b and c, the belt 9 is kept in snug contact with the drum surface along these locations as it passes about the drum in the direction of the arrow 9'. Due to the suction, acting through the porous belt 3, a layer of mica particles is deposited upon the belt and is kept attached thereto when the belt passes upwardly out of the pulp bath in vessel 6. The suction effective in the cells located at b and c then removes the excess water from the deposited mica foil. Since no suction is effective in each cell as it passes through the location d, the web 9, together with the deposited mica foil 18, is lifted or blown off the drum structure 14 and passes through a drying oven 1 1 when leaving the oven 11. The mica foil is completely dry and hence can readily be lifted off the belt 9 to be wound up as a continuous sheet or tape onto a drum or reel 12. The belt 9 of web material passes back to the suction drum, and the cycle repeats itself as described in the foregoing.

. FIG. 2 is a face view of the top surface of the longitudinally creped mica foil according to the invention.

FIG. 3 is a cross section of the mica foil according to FIG. 2 taken along the line Ill lll.

FlG. 4 is a face view of the top surface of the crosswise creped mica foil according to the invention.

The thickness of the mica foil is from 0.02 to 0.2 millimeters. The preferred range is 0.1 millimeter.

The extensibility of the creped mica foil is to 60 percent, preferable 30 percent and the strength is 3 kg/mm at least 1.5 kglmm Crepe paper. is preferred as the shaping and backing material. Crepe paper is paper made to resemble crepe, as by crowding the wet paper sheet on a roll. Crepe itself is a thin crinkled fabric of silk, wool, cotton or rayon.

I claim:

1. Method of producing stretchable creped mica foil which comprises depositing a mica-suspension upon a web of creped material selected from the group consisting of fiber paper and textile material, and subsequently drying the mica suspension on the web.

2. Method according to claim 1, wherein the web material consists of crepepaper and the method includes placing a sheet of the crepe paper onto a backing of foraminous material, contacting the paper-backed material with the mica suspension which is in the form of a watery pulp of mica splittings, and sucking the watery pulp against the paper and thereby sucking the water through the foraminous material to produce a layer of the mica on the paper.

3. Method according to claim 1, wherein the mica consists of fine scale-shaped splittings and the creped web is liquid penn'eable, and the method includes disposing the liquidpermeable creped web against a screen, immersing the webcovered screen into a liquid body comprising the suspension of mica splittings, the web facing downwardly and the screen being above the web, applying suction upwardly through the screen during an immediately following interval in which the web has emerged from the liquid, whereby a layer of mica is formed on the web, removing the micacarrying web from the screen, and repeating the immersion and suction cycle of the screen while subsequently drying the mica suspension on the web.

4. Method according to claim 1, wherein the mica consists of fine scale-shaped splittings and the creped web is continuous and liquid permeable, and the method is continuous and includes disposing part of the continuous liquid-permeable, creped web on a rotary screen, part of the circumference of the rotary screen and part of the so-disposed web being submerged in a liquid body comprising the suspension of mica splittings, forming a mica layer on the web by applying suction to the inside of the screen over the part of its circumference that is submerged and to a part that is not submerged, the web overlying and being supported on the part not submerged and underlying the submerged part, turning the screen and moving the web, carrying the layer of mica on its upper face, to a drying zone, and removing the dried layer of mica foil crepe from the web and returning the web to underlie the submerged part of therotary screen.

5. Method according to claim 1, wherein the web material is liquid-permeable and the mica consists of fine scale-shaped splittings, and the method includes placing the liquid-permeable creped web pnto a backing of foraminous material, immersrng the web in a liquid body comprising the suspension of mica splittings, and sucking liquid suspension from the liquid body against the web and thereby sucking liquid through the material while the web is immersed to produce a layer of the mica on the web.

6. Stretchable crepe mica foil having a cross-sectional shape similar to that of crepe paper, the mica foil consisting essentially of mica splittings.

7. The foil according to claim 6, having a thickness of about 0.02 to 0.2 millimeters.

8. The foil of claim 6, wherein the opposite faces of the mica foil have mutually congruent hills and valleys.

9. Method according to claim 1, which comprises removing the dried mica suspension in the form of a layer of creped mica foil from the web, applying a bonding agent of electrically insulating material to portions of the layer, and superimposing the portions of the layer on one another for securing the layer portions to one another.

10. An electric insulating material comprising superimposed layers of crepe mica foil having crinkled surfaces, said foil consisting essentially of mica splittings, and a layer of bonding substance located between adjacent layers of crepe mica foil for securing said layers of crepe mica foil to one another.

11. Method according to claim 1, which comprises removing the dried layer of creped mica foil from the web, applying bonding agent of electrically insulating material to the layer of creped mica foil, and coiling the layer of creped mica foil into the shape of an insulating part so that adjacent coiled portions of the layer of creped mica foil are secured to one another by the bonding agent therebetween.

12. A laminate comprising a layer of crepe web material and a creped mica foil layer in intimate contact therewith, said foil layer being formed of mica splittings disposed on the hills and in the valleys of the crepe web material. 

2. Method according to claim 1, wherein the web material consists of crepe paper and the method includes placing a sheet of the crepe paper onto a backing of foraminous material, contacting the paper-backed material with the mica suspension which is in the form of a watery pulp of mica splittings, and sucking the watery pulp against the paper and thereby sucking the water through the foraminous material to produce a layer of the mica on the paper.
 3. Method according to claim 1, wherein the mica consists of fine scale-shaped splittings and the creped web is liquid permeable, and the method includes disposing the liquid-permeable creped web against a screen, immersing the web-covered screen into a liquid body comprising the suspension of mica splittings, the web facing downwardly and the scrEen being above the web, applying suction upwardly through the screen during an immediately following interval in which the web has emerged from the liquid, whereby a layer of mica is formed on the web, removing the mica-carrying web from the screen, and repeating the immersion and suction cycle of the screen while subsequently drying the mica suspension on the web.
 4. Method according to claim 1, wherein the mica consists of fine scale-shaped splittings and the creped web is continuous and liquid permeable, and the method is continuous and includes disposing part of the continuous liquid-permeable, creped web on a rotary screen, part of the circumference of the rotary screen and part of the so-disposed web being submerged in a liquid body comprising the suspension of mica splittings, forming a mica layer on the web by applying suction to the inside of the screen over the part of its circumference that is submerged and to a part that is not submerged, the web overlying and being supported on the part not submerged and underlying the submerged part, turning the screen and moving the web, carrying the layer of mica on its upper face, to a drying zone, and removing the dried layer of mica foil crepe from the web and returning the web to underlie the submerged part of the rotary screen.
 5. Method according to claim 1, wherein the web material is liquid-permeable and the mica consists of fine scale-shaped splittings, and the method includes placing the liquid-permeable creped web onto a backing of foraminous material, immersing the web in a liquid body comprising the suspension of mica splittings, and sucking liquid suspension from the liquid body against the web and thereby sucking liquid through the material while the web is immersed to produce a layer of the mica on the web.
 6. Stretchable crepe mica foil having a cross-sectional shape similar to that of crepe paper, the mica foil consisting essentially of mica splittings.
 7. The foil according to claim 6, having a thickness of about 0.02 to 0.2 millimeters.
 8. The foil of claim 6, wherein the opposite faces of the mica foil have mutually congruent hills and valleys.
 9. Method according to claim 1, which comprises removing the dried mica suspension in the form of a layer of creped mica foil from the web, applying a bonding agent of electrically insulating material to portions of the layer, and superimposing the portions of the layer on one another for securing the layer portions to one another.
 10. An electric insulating material comprising superimposed layers of crepe mica foil having crinkled surfaces, said foil consisting essentially of mica splittings, and a layer of bonding substance located between adjacent layers of crepe mica foil for securing said layers of crepe mica foil to one another.
 11. Method according to claim 1, which comprises removing the dried layer of creped mica foil from the web, applying bonding agent of electrically insulating material to the layer of creped mica foil, and coiling the layer of creped mica foil into the shape of an insulating part so that adjacent coiled portions of the layer of creped mica foil are secured to one another by the bonding agent therebetween.
 12. A laminate comprising a layer of crepe web material and a creped mica foil layer in intimate contact therewith, said foil layer being formed of mica splittings disposed on the hills and in the valleys of the crepe web material. 